Intestinal inflammation alters mucosal carbohydrate foraging and monosaccharide incorporation into microbial glycans

Abstract

Endogenous carbohydrates released from the intestinal mucus represent a constant source of nutrients to the intestinal microbiota. Mucus-derived carbohydrates can also be used as building blocks in the biosynthesis of bacterial cell wall components, thereby influencing host mucosal immunity. To assess the uptake of endogenous carbohydrates by gut microbes in healthy mice and during intestinal inflammation, we applied azido-monosaccharides that can be tracked on bacterial cell walls after conjugation with fluorophores. In interleukin-10 deficient mice, changes in the gut microbiota were accompanied by decreased carbohydrate hydrolase activities and increased lumenal concentrations of host glycan-derived monosaccharides. Tracking of the monosaccharideN-azidoacetylglucosamine (GlcNAz) in caecum bacteria revealed a preferential incorporation of this carbohydrate byXanthomonadaceaein healthy mice and byBacteroidaceaein interleukin-10 deficient mice. These GlcNAz-positiveBacteroidaceaefractions mainly belonged to the speciesB. acidifaciensandB. vulgatus. Growth ofBacteroidesspecies in the presence of specific monosaccharides changed their stimulatory activity toward CD11c(+)dendritic cells. Expression of activation markers and cytokine production was highest after stimulation of dendritic cells withB. vulgatus. The variable incorporation of monosaccharides by relatedBacteroidesspecies underline the necessity to investigate intestinal bacteria down to the species level when addressing microbiota-host interactions.